If your rub has a lot of sugar, higher temps will turn it dark no matter what kind of cooker you use. Here are some ideas:
1. Use turbinado sugar in the rub (processed from cane juice). It tolerates higher temperatures better.
2. Use the classic 3-2-1 approach with bare rubbed meat first, then foil, then unwarpped to set sauce. The wrap will help keep the rub from darkening but try to stay below 300. Remember that the numbers do not stand for hours, but for relative timing. Everyone's cooker is different in terms of cavity temperature.
How do you like the finished product? Firm and pull, or "fall off the bone"? There are different ways to get there.
Good cookin' to ya'
Hub